FAA Inspection Mandates Target Subset Of Boeing 787s

The FAA has finalized an inspection plan for a subset of Boeing 787s produced from 2013-2017 that may have improper shimming in several areas. 

Two airworthiness directives (ADs) set for publication Dec. 6 mandate the inspection protocol for affected operators, adopting sets of Boeing-recommended initial and repetitive checks first released to operators in September 2020. 

Both sets of mandates were “prompted by reports that shimming requirements were not met during the assembly of certain structural joints, which can result in reduced fatigue thresholds and cracking of the affected structural joints,” the FAA ADs said. 

The FAA directive applies to 79 U.S.-registered aircraft—part of a subset of about 500 affected 787s that Boeing listed in September 2020 service bulletins that identified the issues and recommended inspections. All affected airframes range from between manufacturer line nos. 115 and 619, and are either 787-8s or 787-9s. The issues covered in the bulletins and new ADs were corrected before Boeing began producing 787-10s in 2017, so none of the 787 family’s largest members have the issues. 

Shimming, or filling small gaps between assembled pieces of airframe or parts, is a regular part of aircraft construction. Incorrect shimming, such as by missing gaps or installing incorrectly sized shims, creates risk of stress build-up between the parts. Over time, this can cause cracking or other problems. 

Improper shimming has plagued the 787 program from the beginning. A broad 2013 FAA review of the 787-8’s design, certification and production prompted by the model’s grounding due to issues with lithium-ion batteries cited “discrepant shimming” on the aft fuselage and horizontal stabilizer as an issue to address.  

More recently, improper shimming between fuselage sections led Boeing to dig deeper into the issue, extending the probe to suppliers. The latest findings, including non-conforming shims, caused Boeing to pause 787 deliveries in October 2020 and again in April 2021 while it focuses on developing reliable inspection methods to determine where problems exist on undelivered aircraft. That work—and the delivery pause—is still ongoing, and has prompted some U.S. lawmakers to scrutinize FAA’s oversight of the issues. 

An improper shimming issue rarely poses an immediate safety-of-flight risk unless it is combined with other issues. Boeing last year found eight aircraft with shim issues and a composite skin quality problem, prompting the manufacturer to recommend immediate repairs. 

While the latest directives address shimming issues, the problems are not connected to the current delivery hold-up, nor are they immediate safety risks. Inspection thresholds and airframe utilization histories suggest the first checks are likely a decade away at least. 

One directive targets areas around aft wheel well bulkhead (AWWB), a large composite structure running transversely across the lower section of the fuselage close to the junction of the wing trailing edge. The mandate calls for high frequency eddy current (HFEC) inspections for cracking of the forward edge of the bulkhead’s side fitting at Station 1290 on both sides of the fuselage, the side fitting outer chord and fail-safe strap areas, as well as the body chord itself. Similar checks are required for cracking of the AWWB’s body chord forward edge “and around all the fastener heads and vertical beam clips common to the AWWB body chord horizontal flange,” the directive said.

The second directive targets possible cracking of certain areas of the pickle fork—or wing spar-to-fuselage joint that provides an active suspension between the wing and airframe—at Station 873. Among the specific checks are HFEC inspections around all fasteners common to the front spar pickle fork outer chord surface between stringer S-22 and stringer S-24. It also calls for ultrasonic inspections along certain areas of the pickle fork outer chord end fittings. 

Compliance time for the initial inspections is based on service life. The pickle-fork checks must be done before aircraft have reached 101,000 flight hours or 28,000 cycles. Aviation Week Fleet Discovery shows few of the affected aircraft had reached 30,000 flight cycles as of July 31, and none had reached 7,100 cycles. The fleet leader among the affected models in both categories, a Qatar Airways 787-8 delivered in 2013, had about 37,000 hours and 7,030 cycles. 

Boeing also provided a formula that factors in flight lengths for calculating a deadline, giving operators more flexibility without adding risk. American Airlines and United Airlines told the FAA that their aircraft utilization tracking cannot handle the formulas, and requested they be replaced with modified hours-and-cycles limits that factor in stage lengths. 

“The current compliance data would require the use of the most conservative values or constant monitoring of aircraft utilization,” American said in comments on a draft version of the rule. The airline suggested “the FAA include simplified limits ... allowing operators to maximize the hours and cycle threshold.” 

The request was rejected.  

Flight-length sensitive deadlines “were developed with the flexibility to take advantage of individual aircraft utilization,” the agency said. “An operator may choose to develop simplified thresholds, provided they are at or below the required compliance times.”